Many of the airbag passive restraint systems used in modern vehicles rely on inflators which produce the gas needed to inflate the airbag by ignition of gas generant compositions. These compositions, once heated to their ignition temperature, combust to produce a large amount of gas in a relatively short period of time, thereby providing for the required rapid inflation of the airbag. It is also important that they provide the long term reliability required of airbag systems, which are expected to perform properly over the lifetime of the vehicle in which they are installed.
Recently, the most commonly used gas generant compositions have involved azide compounds, such as sodium azide, as the fuel component. As more fully explained in U.S. Pat. No. 3,741,585, these compositions provide long term reliability, relatively low reaction temperatures during the gas generation step, and non-toxic gas products. These compositions, however, are themselves toxic and are easily hydrolyzed. As explained in U.S. Pat. No. 4,369,079, they also readily react with heavy metals, such as copper, lead, etc., to form sensitive materials which are subject to unexpected ignition and detonation. These problems have led to the development of further gas generant compositions, such as the tetrazole and nitrotriazalone based compositions described in U.S. Pat. Nos. 4,369,079 and 4,931,112. The newer compositions, while described as providing a low temperature burn, nevertheless burn at temperatures significantly above the 200.degree. to 1000.degree. F. temperatures attributed to the azide based compositions in the previously noted U.S. Pat. No. 3,741,585. These newer compositions are part of a class of compositions which is often referred to in the art either as non-azide generants or as high reaction temperature generants. Hereinafter, we shall refer to this class of compounds as high reaction temperature generants.
A variety of materials have been used as the structural material in inflator housings, including steel, stainless steel and aluminum. Recently, aluminum has been favored due to its relative weight advantage, its long term corrosion resistance and its relative ease of processing. A particularly advantageous inflator, and method of fabricating such incorporating inertial welding, is described in U.S. Pat. No. 4,547,342.
All of the patents mentioned above are owned by the assignee of this application and are hereby incorporated by reference herein.
Testing of developmental prototypes of inflators similar to those described in U.S. Pat. No. 4,547,342, wherein gas generating materials within the non-azide or high reaction temperature generant category are used, has resulted in occasional localized failures of the inflator housing structure. It is an object of the present invention to provide inflator housing structures which are protected against such failures.
A related invention is described in U.S. patent application Ser. No. 08/411,002, filed on Mar. 27, 1995, and entitled "An Airbag Inflator With Components Protected From High-Temperature, Reactive Generated Gases". That application is assigned to the same assignee as is this case, and is incorporated by reference herein.